1. Field of the Invention
This invention relates to a novel plural fluid combined magnetic/centrifugal seal.
More particularly, this invention relates to a novel combined centrifugal and magnetic seal structure which employs separate, different viscosity fluids for use during separate magnetic seal and centrifugal seal operating modes of the structure whereby each seal complements the other at different rotational speeds. The plural fluid/magnetic/centrifugal seal makes it possible for the design parameters of each seal stage, though coacting over a complete speed range, to be substantially independent one from the other and optimized design criteria can be employed in the construction of the two cooperating seals.
2. Background of Invention
A combined magnetic/centrifugal seal is described and claimed in U.S. patent application Ser. No. 140,969, filed Apr. 17, 1980 for a "Magnetic/Centrifugal-Fluid Seal" in the name of Donald F. Wilcock et al. and assigned to Mechanical Technology, Inc. The combined magnetic/centrifugal seal disclosed in U.S. patent application Ser. No. 140,969 employs a ferromagnetic fluid which in conjunction with a magnetic seal gap region of the structure, provides magnetic sealing for speed ranges from zero to rotational speeds of about 2000 revolutions per minute (rpm). At higher rotational speeds above about 2,000 rpm the same ferromagnetic fluid provides through centrifugal effects on the fluid a centrifugal sealing action for speed ranges from about 2000 rpm to 20,000 rpm. At the higher rotational speeds, however, cooling of the ferromagnetic sealing fluid is required in order that its magnetic sealing capabilities not be adversely affected by the high temperatures encountered at higher rotational speeds. It will be appreciated therefore that the upper rotational speeds at which the combined magnetic/centrifugal seals of the type described in application Ser. No. 140,969 can be driven, in effect is limited by the temperature characteristics of the ferromagnetic fluid and the ability to design into the seal structure effective cooling for the ferromagnetic fluid. To overcome these limitations, the present invention was devised.